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KDESC 4.3+: Video, Music, Image and Document Preview in Dolphin

"In most distributions that come with KDE Software
Compilation 4.3 and above, opening Dolphin for browsing the
filesystem will give you this window:

"The left circle shows the Preview Mode Button. We will expand
on this option below.

"On the right is the Information Panel, which in addition to
showing info about the file (type, size, modified etc.), will allow
you to preview the majority of files (Text, Image, PDF, Open
Document). This happens after you select a file or hover your mouse
over it."